HEAT stress in cattle can become a major issue both for animal production levels and animal welfare.
Department of Primary Industries (DPI) District Veterinary Officer Jeff Cave said the ideal temperature range for cattle was between 5 and 25°C, but as the temperature rises, it becomes more difficult for cattle to cool themselves.
“High producing dairy cows are sensitive to heat stress because of their high feed intake,” Dr Cave said.
“At temperatures above 27°C, cattle have to redirect energy away from production to help cool them; this is done via heat loss through their skin and lungs.
“Feed intake is also reduced and, as the temperature rises above 32°C, a more dramatic decrease in milk production may be observed.”
Humidity can also play a significant role in heat stress and for any given temperature, the degree of heat stress increases as the relative humidity increases.
There are three temperature-humidity ranges of concern:
A temperature of 38°C and 20 percent humidity is the range to begin serious measures to ease the heat stress on cattle - some type of cooling should be started.A more dangerous situation is when the temperature nears 38°C and the humidity 50 percent.The lethal range for cattle is 38°C and a humidity of 80 percent.Heat stressed cattle may show some of the following signs:
seeking out shade, which they often will not leave to drink or eat;increased water intake;reduced feed intake;standing rather than lying down;increased respiratory rate;increased body temperature;increased salivation;reduced milk production;reduction in observable heat behaviour; and/orreduction of conception rates.Dr Cave said while it’s not possible to eliminate the effect of heat stress, there are a number of management factors, which can reduce its effects.
These include:
on hot days, placing cattle in paddocks where they have access to adequate amounts of shade;ensuring that cattle have adequate access to good quality, cool drinking water;allowing cattle to take their time when moving;avoiding overcrowding in yards; andproviding cattle with better quality feed during the evening (when it is cooler, and the cattle are likely to have better intakes).For dairy cows:
slightly modifying the times of milking so that milking is completed early in the morning before it gets too hot and holding milking back to the cooler part of the evening;sprinklers can be set up in the milking yard to cool cows while they wait to be milked; andlarge fans in the milking shed can help keep the operator and the cows a little cooler.“While heat stress can have significant impacts on production and animal welfare, by making some minor management changes and taking a little extra care of your cattle in extreme hot weather the effects of heat stress on herds can be substantially reduced,” Dr Cave said.
For further information please contact your local veterinarian or DPI veterinary or animal health officer, or in NSW your Rural Lands Protection Board.
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